1. Technical Field
This invention relates to a travel route generating method for an unmanned vehicle and, in particular, to a method of generating a travel route capable of minimizing a traveling cost of the unmanned vehicle.
2. Related Art
Unmanned vehicle driving systems are introduced in wide-area working sites such as quarrying sites and mines so that unmanned vehicles, in place of manned vehicles such as manned off-road dump trucks, perform soil transportation works in order to avoid accidents due to worker fatigue, to achieve laborsaving, and to improve productivity by enabling extended working time.
Outlines of unmanned vehicle driving systems will be described below.
A working site includes various areas such as loading sites, dumping sites, filling stations, and parking lots. These areas are interconnected by well-prepared transportation roads called haul roads, and lead-in roads, called access roads, extending from the haul roads to the areas, as well as by intersections.
A loading site is a place where soil is loaded on dump trucks. Specifically, excavation work is performed by excavation vehicles such as wheel loaders (front-end loaders), backhoes, and shovels, and loading work is performed to load soil on dump trucks.
A dumping site is a place where soil loaded on dump trucks is discharged either at a fixed position or at regular positions within the area. When soil is discharged at a fixed position, the soil is discharged into a hopper provided with a rock crushing machine called crusher. In some cases, at a dumping site, discharged soil is leveled out by a dozer. In such cases, the dozer may indicate positions to discharge soil in order to repair damaged road surfaces so that the soil is discharged at the indicated soil discharging positions.
A filling station is provided with a fuel pump. The filling station is often attached to a parking lot. Even if dump trucks are supposed to be fueled from a fuel truck, the filling station may be provided so as not to impede operation of other dump trucks.
A parking lot is a place where when vehicles are manned vehicles used for manned work, the vehicles are parked so that the operators take a meal or are relieved. As for an unmanned vehicle driving system, a parking lot is a place where dump trucks are stored to allow inspectors to step into dump trucks safely for conducting periodic inspections or the like, and to allow operators to perform start operation.
Various methods of generating travel routes for unmanned vehicles have been tried, which will be described below.
[Route Generating Method by Teaching]
When a travel route including haul roads, access roads, intersections and crushers can be fixed, a dump truck is actually driven by an operator before starting work so that travel trajectory data obtained during this run is stored in memory.
[Route Generating Method Based on Drawings]
A travel route is predetermined by previous calculation based on plans of sites such as a mine and so on.
According to the route generating method by teaching described above, however, various data must be obtained by manpower by previously running a vehicle before starting work. Thus, this method requires a lot of time and labor for generating a travel route, impairing the work efficiency as a whole.
Above all, in actual loading sites and dumping sites, loading positions and soil discharging positions will be changed in a complicated manner according to development of the work, and the size and geometry of each loading site also will be changed along the development of the work. Therefore, it is impossible to predetermine a travel route. Specifically, the travel route must be generated from time to time such that a work vehicle such as a dozer can reach a soil discharging position indicated by its operator in the course of work, or such that it can reach a soil discharging position and a loading position which are obtained by calculation based on the area geometry which changes every second according to the development of the work. The route generating method based on drawings described above also suffers from the same problems.
In order to overcome these problems, techniques to generate a route by data simulation have been tried.
The following techniques are known as route generating techniques. These route generating techniques have been studied in the field of robotics.
a) Route generation by combination of circular arcs and straight lines
This is a method to generate a travel route by combining straight lines, circular arcs and so on, using mesh and vector potential. A method using random search is also available.
b) Route generation by Clothoid curve maintaining curvature continuity
c) Route generation by polynomial curve
The present applicant and others have already conceived an invention and applied for a patent, relating to a method of automatically generating a travel route for an unmanned vehicle when data on a travel route generation range for the an unmanned vehicle are given by means other than teaching, and this method is well known.
Japanese Patent Application Laid-Open No. 11-296229 describes an invention according to which information on an obstacle detected by one unmanned vehicle is shared by several unmanned vehicles as common obstacle information, and a travel route is generated so as to avoid the obstacle.
Japanese Patent Application Laid-Open No. 2000-137522 describes an invention according to which when a soil discharging region is given, a plurality of target soil discharging points are set in the soil discharging region, and a plurality of travel routes are generated to reach these target discharging points.
When the route generating techniques described in (a), (b), and (c) above are applied to travel route generation for unmanned vehicles, the time required for travel route generation will be shortened in comparison with the route generating method by teaching or the like. However, these techniques pose various problems when taking into consideration the controllability of the unmanned vehicles and the productivity.
If these conventionally techniques are directly applied to an unmanned vehicle driving system, even minimum vehicle constraint conditions cannot be satisfied in some cases.
For example, the route generating method using mesh and vector potential as described in (a) above does not take into consideration turning radii of vehicles. Therefore, there will be a chance that an unmanned vehicle cannot turn around in a travel route generated by this method, making it impossible to run the vehicle.
According to another conventional technique using random search, the algorithm depends on random numbers, which makes it difficult to find the cause of trouble when travel route generation becomes impossible.
Furthermore, travel routes generated by these conventional techniques are not necessarily optimal routes in terms of cost.
Specifically, in actual working sites, it is desirable that the frequency of replacing consumable parts and the occurrence of failure should be minimized to reduce the costs caused by running unmanned vehicles so that the unmanned vehicles are enabled to operate for a long period of time with high reliability. In particular, dump truck tires are so expensive that it is imperative to reduce the load on the tires. Further, it is desirable for achieving the cost reduction that the time required for traveling the vehicle should be shortened to reduce the working time and the vehicle's operating time. It is also desirable for achieving the cost reduction that the vehicles are enabled to travel with low fuel consumption.
Therefore, it becomes an important issue how to generate a travel route minimizing the costs caused by travel of unmanned vehicles. Specifically, for example, these unmanned vehicles are desirably capable of reducing the load on tires and vehicle bodies, shortening the time required for the travel, and traveling with low fuel consumption. More specifically, the traveling cost can be reduced if smooth steering operation is possible and the acceleration and deceleration levels on the vehicle bodies are low, and thereby the load on the tires or vehicle bodies can be suppressed. Further, the traveling cost can be reduced if the time required for the travel of the vehicle is shorted and thereby the working time and the vehicle's operating time are reduced. Still further, the traveling cost can be reduced if the vehicle can travel along the travel route with low fuel consumption.
None of the conventional techniques generates an optimal travel route taking into consideration the costs caused by travel of a vehicle as described above. For example, according to the route generating method using combination of circular arcs and straight lines described in (a) above, the curvature becomes discontinuous at connection points between the circular arcs and the straight lines, which may oblige reduction of vehicle speed or forcible steering operation. Therefore, the work efficiency is poor and the productivity is low.
Likewise, according to the route generating method using a Clothoid curve for maintaining curvature continuity described in (b) above and the route generating method using a polynomial curve described in (c) above, although the curvature continuity is ensured to a certain degree for a single curve, discontinuity in curvature or in rate of change of curvature will occur at the joint when a curve is joined to another one. This will also pose a problem of reduced productivity because reduction of vehicle speed or forcible steering operation may be obliged at the joint between the curves.
When an unmanned vehicle changes its traveling direction in a narrow working site, a switchback point must be included in the travel route. However, according to the conventional techniques, the switchback point positions are set in a fixed pattern. This poses a problem in terms of versatility. Specifically, since the switchback points are set uniformly in a fixed pattern, the travel route containing such switchback points is not optimal one that enables reduction the traveling cost.
This invention has been made in view of these circumstances. It is an object of the invention to minimize the vehicle traveling cost by generating an optimal travel route capable of satisfying the minimum constraint conditions for a vehicle to run and yet capable of minimizing the load on the tires and the vehicle body, shortening the time required for the vehicle to travel, and enabling the vehicle to travel with low fuel consumption.
It should be understood that the inventions described in Japanese Patent Application Laid-Open Nos. 11-296229 and 2000-137522 do not take into consideration the costs caused by running vehicles when generating a travel route.